This invention relates generally to fluid handling devices, specifically to magnetically actuated devices employing slugs made of a magnetic fluid to control fluid movement through microsized flow channels.
Miniature fluid handling devices to control fluid movement, which include micropumps and microvalves for use in microfluidic devices, can be constructed using fabrication techniques adapted from those applied to integrated circuits. Microfluidic devices have environmental, biomedical, medical, biotechnical, printing, analytical instrumentation, and miniature cooling applications.
Several different kinds of micropumps exist that can control flow on the order of microliters per minute (S. Shoji and M. Esashi (1994), xe2x80x9cMicroflow Devices and Systemsxe2x80x9d, J. Micromech. and Microeng.4:157-171). Micropumps with moving parts include peristaltic pumps and reciprocating pumps. These reciprocating pumps have a pressure chamber with a diaphragm driven by an actuator and passive check valves. Passive micropumps with no moving parts include electrohydrodynamic, electro osmotic, and ultrasonic pumps. U.S. Pat. No. 5,876,187 describes methods of making micro machined pumps.
Electroosmotic pumps, which rely on the use of chargeable surfaces within the pump, are generally applied to fluid handling in microsized systems (D. J. Harrison et al. (1992), xe2x80x9cCapillary Electrophoresis and Sample Injection Systems Integrated on a Planar Glass Chipxe2x80x9d, Analytical Chemistry, 64 (17): 1926-1932). Chargeable surfaces have a fixed charge on their surface when in contact with an appropriate fluid. Electro osmotic pumping also requires the presence of counterions in the fluid adjacent the charged surface. Appropriate application of an electric field to a channel having a chargeable surface causes flow of the counterions of the fluid in the channel and as a result flow of the fluid as a whole to effect pumping in the channel. However, the pumping rate is dependent upon the pH, ionic strength and ion concentration of the fluid. Electro osmotic pumping may not be useful for applications where these fluid properties change or where they are unknown.
U.S. Pat. Nos. 4,967,831 and 5,005,639, both issued to Leland, disclose magnetically actuated macrosized piston pumps that in one embodiment use a magnetically confined ferrofluid slug as a self-sealing and self-repairing pump piston. The pumps were described for use in heat pipes. There is no description of the use of these pumps in microfluidic systems. The pumps described employ permanent ring magnets and electromagnets surrounding a conduit, but this configuration cannot readily be adapted to microconduits.
Ferrofluid slugs have recently been used as seals in micro fabricated valves and as pistons in microfabricated pumps (H. Hartshorne et al., xe2x80x9cDevelopment of Microfabricated Valves for xcexcTASxe2x80x9d, MicroTAS Conference Proceedings, Banff, Alberta, Canada, October 1998, pp. 379-381; H. Hartshorne et al., xe2x80x9cIntegrated Microfabricated Ferrofluidic Valves and Pumps for ATASxe2x80x9d, poster presented at DARPA Conference, Dec. 3, 1998, San Diego, Calif.; H. Hartshorne et al., xe2x80x9cMicrofabricated Ferrofluidic Valves and Pumpsxe2x80x9d, poster presented at DARPA Conference, Jul. 31, 1999, Pittsburgh, Pa.). The references report valving of gases and liquids and pumping of gases, but not liquids. The pump design described has a ferrofluid piston moving in a side channel separate from the flow channel containing the fluid inlet and outlet. Therefore, this piston is unable to also act as a valve in the main flow channel where the inlet and outlet are located.
Ferrofluids have been used in the design of magnetic pipettes (Greivell, N. E. and Hannaford, B. (1997), xe2x80x9cThe Design of a Ferrofluid Magnetic Pipette,xe2x80x9d IEEE Transactions on Biomedical Engineering 44(3):129-135).
Macroscale pumps have been attempted using ferrofluids as described in C. W. Miller (1974), xe2x80x9cMagnetic Fluids: Magnetic Forces and Pumping Mechanisms,xe2x80x9d Ph.D. Thesis, Cornell University, however such pumps require special coatings and seals not required by the present invention.
The present invention is generally directed to magnetically actuated fluid handling devices employing slugs made of a magnetic fluid to move a fluid through microsized flow channels. These fluid handling devices include micropumps and microvalves.
In a first embodiment, this invention provides a fluid handling device having at least one microsized flow channel in fluid communication with at least one fluid inlet and at least one fluid outlet. At least one slug of magnetic fluid is located within the flow channel and can be held stationary by a magnet to block fluid flow through the flow channel. The slug can also be moved by a magnet to pull or push fluid through the flow channel.
In other embodiments of this invention, the device described above can incorporate additional features to allow a variety of fluid handling operations. For example, a fluid handling device can incorporate one or more inlets and outlets for magnetic fluid slugs to enter and leave the flow channel. A slug inlet can be connected to a source of magnetic fluid to allow two or more slugs separated by fluid to be generated. A slug outlet allows a slug to be pulled out of the way of the fluid behind it. One or more air vents may also be incorporated into these devices to facilitate separation of slugs from a reservoir of magnetic fluid with air and to alternate different fluids in the flow channel.
One primary advantage of the fluid handling devices described herein over other micropumps is that the magnetically actuated slug moves within the flow channels of the microfluidic device to facilitate valving and/or pumping of fluid and no separate pump is required.
In another embodiment, this invention provides a fluid handling device having at least one microsized flow channel forming a loop. The flow channel is in fluid communication with at least one fluid inlet and at least one fluid outlet, including a first fluid inlet and a last fluid outlet which are adjacent, yet separated by a channel volume, from each other along the fluid channel loop. The device also has at least two slugs of magnetic fluid, both located within the flow channel loop. At least one slug is moved around the flow channel loop by a magnet to pull and push fluid from fluid inlets towards fluid outlets of the flow channel loop. The slug is moved in the loop passing the first inlet, any intermediate outlets and inlets, past the last outlet, and through the channel volume separating the last outlet from the first inlet. At least one slug is held stationary by another magnet between the last fluid outlet and the first fluid inlet to block fluid flow through the flow channel loop back into the first fluid inlet. The moving slug of magnetic fluid merges with and passes through the stationary plug of magnetic fluid as it moves around the fluid channel loop. The combined action of the slugs in the channel has the net effect of pumping fluid from the fluid inlets and to the fluid outlets and particularly from the first fluid inlet to the last fluid outlet. The volume of the stationary slug is preferably less than the channel volume between the last fluid outlet and the first fluid inlet, except when the stationary slug is merged with the moving slug. The volume of the moving slug is preferably less than the channel volume between the most closely spaced fluid inlet and outlet in the channel loop, so that adjacent inlets and outlets along the loop channel are not both blocked by the moving slug. Also, if two or more sets of fluid inlets and outlets are present, at least two moving slugs are used.
One embodiment of this invention takes advantage of the shape-changing capabilities of magnetic gels, which are also magnetic fluids as defined herein, to form valves and pumps. Such magnetic gels are described, e.g. in Szabo, D. et al. (1998), xe2x80x9cShape Transition of Magnetic Field Sensitive Polymer Gels,xe2x80x9d Macromolecules 31:6541-6548.
In all the embodiments of this invention, the magnets for holding or moving the magnetic slug(s) may be located on one side or both sides of the flow channel assembly, rather than surrounding the flow channels, simplifying assembly of the microfluidic device. In addition, the magnets used to control the magnetic fluid slug movement can be either individual magnets moved along the flow channels in a flow channel assembly or an array of magnets mapping the flow channel assembly whose elements can be individually controlled to hold or move a magnetic slug. For example, using an array of electromagnets, magnets positioned along a flow channel can sequentially be turned on and off to create the same effect as a magnet moving along the flow channel. Alternatively, magnetic fields can be generated at selected points within the flow channel.
Methods for using the fluid handling devices of this invention as well as microfluidic devices employing one or more fluid handling devices of the present invention are also provided. These microfluidic devices may combine the fluid handling devices of the present invention with microfluidic devices already described in U.S. Pat. No. 5,922,210 (Tangential Flow Planar Microfabricated Fluid Filter and Method of Using Thereof), U.S. Pat. No. 5,716,852 (Microfabricated Diffusion-Based Chemical Sensor), U.S. Pat. No. 5,972,710 (Microfabricated Diffusion-Based Chemical Sensor), U.S. Pat. No. 5,948,684 (Simultaneous Analyte Determination and Reference Balancing in Reference T-Sensor Devices), U.S. patent applications Ser. No. 09/346,852 (Microfabricated Differential Extraction Device and Method), Ser. No. 08/823,747 (Device and Method for 3-Dimensional Alignments of Particles in Microfabricated Flow Channels), Ser. No. 08/938,093 (Multiple Analyte Diffusion-Based Chemical Sensor), U.S. Pat. No. 6,007,775 (Multiple Analyte Diffusion Based Chemical Sensor) (Separation and Chemical Reaction), U.S. Pat. No. 5,948,684 (Simultaneous Analyte Determination and Reference Balancing in Reference T-Sensor Devices), U.S. patent application Ser. No. 09/080,691 (Liquid Cartridge Analysis), and U.S. Pat. No. 5,971,158 (Absorption-Enhanced Differential Extraction Device).
The fluid handling devices of the present invention can handle gases and liquids simultaneously. Therefore, these fluid handling devices can be made self priming. In addition, these devices are more resistant to nonuniformities in fluid input than other types of micropumps which need to be tuned to pump either liquid or gas. For example, in reciprocating pumps employing a piezoelectric actuator, the piezoelectric material is set to resonate at a given frequency which depends upon the compressibility of the medium being pumped.